# 8 Newsletter of the International DORIS Service December 2020

2020 celebrates DORIS was first carried on the SPOT-2 satellite, which recorded the first DORIS measurements on 3 February 1990. Since then, the system has operated continuously 30 years on 18 satellites, including the space imaging satellites SPOT-2/3/4/5, Pleiades1A-1B, altimetry missions for ocean of the DORIS observations such as TOPEX-Poseidon, ENVISAT, Jason-1/2/3, HY-2A, Saral/AltiKa, Sentinel3-A/B, and also for hydrological system monitoring and ice measurements with Envisat, Cryosat-2, Saral/AltiKa and Sentinel3-A/B. On the latest missions such 30 years of continuous operations as Sentinel-3A/3B, the DORIS system can achieve radial at the heart of altimetry mission orbit accuracies of 8-10 mm RMS (Root mean square). The performance for oceanography DORIS data are used for both real-time orbit determination and geodetic applications. onboard the satellite, and precise orbits developed with a latency of two days to a few weeks for use with altimeter data provided by these different missions. MOST OF THE DORIS STATIONS ARE CO-LOCATED WITH OTHER SPACE GEODETIC TECHNIQUES AND TIDE-GAUGES

If you want to subscribe Contributions and feedback to the newsletter, please are welcome at any time send an e-mail to Please send them to: ids.central.bureau@ids-doris.org. [email protected] The editors reserve the right december 2020 // Newsletter of the International DORIS Service - 1 - with “Subscribe Newsletter” in the subject. to edit all contributions. THULE, ON THE NORTHWEST COAST OF GREENLAND

The DORIS system (Doppler the geocenter of the Earth. DORIS the absolute variations in sea level Orbitography and Radio positioning is one of the four space geodetic and compare them to the values Integrated by Satellite) was designed techniques that contribute to the obtained by satellite altimetry. and developed in the early 1980s by International Terrestrial Reference 5. DORIS observes and analyses CNES (the French Space Agency), Frame (ITRF). geophysical phenomena such as IGN (Institut Géographique National, earthquakes or periodic inflation the French Mapping and Survey Over the past 30 years, DORIS has and deflation events of volcanoes, Agency) and the GRGS (Groupe de enlarged the scope of its scientific tectonic plate movements, local Recherche de Géodésie Spatiale) applications: ground uplift or subsidence, etc. to determine satellite positions 1. DORIS has contributed to with high accuracy for support monitoring changes in mean sea The DORIS instruments (both on altimetry missions dedicated to level, both regionally and globally, board the satellites and on the ocean monitoring. using data from the TOPEX/Poseidon ground), as well as the DORIS and Jason 1, 2, & 3 missions. This system is based on Doppler shift 2. Through the precise orbits provided THE GREEK DORIS STATION OF measurements of radio-frequency for the Envisat, CryoSat-2, Saral/ DIONYSOS FACING THE AEGEAN SEA signals (400 MHz and 2 GHz) AltiKa and Sentinel3-A/B missions, transmitted by a network of ground the DORIS system has participated stations, used as reference points in monitoring the change in height of on the Earth's surface. There are the Antarctic ice sheet over 25 years. about 60 DORIS stations uniformly 3. DORIS contributes to the distributed around the world, and International Terrestrial Reference these stations are hosted by 48 Frame (ITRF) realization and various international host agencies. maintenance with increased performance each time, In addition to precise orbit 4. The co-location of DORIS with determination, the DORIS system tide gauges allows monitoring on can also locate ground positions the same site the vertical ground with the same intrinsic accuracy. The movements measured by the DORIS data are also used for determination technique and the variations in sea of Earth Orientation Parameters level relative to the ground recorded (EOP), and can be used to determine by the tide gauge in order to deduce

- 2 - Newsletter of the International DORIS Service // december 2020 DORIS STATION AT CROZET ISLANDS, FRENCH SOUTHERN AND ANTARCTIC LANDS

monitoring and control system have THE DORIS STATION OF FUTUNA IN THE PACIFIC OCEAN undergone continual improvement over the years. The centralized CNES/IGN management has made it possible to control the development of the network and more easily achieve its objectives: the DORIS network is today the most homogeneous, stable and durable geodetic network in the world. Most of the DORIS stations are co-located with other space geodetic techniques (Satellite Laser Ranging, Very Long Baseline Interferometry and Global Navigation Satellite Systems) antenna, whose deployments recommendations focus on three and tide-gauges, thus promoting started in 2019. The 3rd generation main themes: technological inter-comparisons antenna (the Starec “C” antennae) ➞ expand the DORIS community; and scientific advances. defines the 2 GHz phase center ➞ evolve the technology; location with a precision of ± 2 mm. ➞ improve infrastructure and In 30 years, the position in orbit Studies are underway for the treatment of data. has been reduced from 13 cm to development of a future miniaturized Some recommendations are already less than 1 cm. The DORIS-DIODE on-board receiver coupling GNSS being implemented; others are in navigator on board the satellites and DORIS signals. preparation. calculates the satellite's trajectory in real time with a radial accuracy of In addition, following the IDS The DORIS system really has a 2 to 3 cm. The DORIS contribution to retreat organized in 2018, the IDS bright future ahead of it and will the ITRF has progressed in the same has drawn up a strategic plan for contribute to the success of many way with new possible applications. the years to come. About twenty future missions. recommendations were presented Further progress is expected in the to stakeholders during the DORIS next decade with the 4th generation steering committee (CNES/ beacon and the 3rd generation IGN) at the end of 2019. These

december 2020 // Newsletter of the International DORIS Service - 3 - IDS AND DORIS MILESTONES

early 1980s 1998 2007 2014 Decision of the realisation Spot-4 (Cnes) with the first STPSat-1: Citris Deployment of Starec of the DORIS system, version of Diode software (Scintillation and ground antennae jointly by the French space for real-time on-board Tomography receiver in with consolidated agency (CNES, Centre orbit determination. space) developped by manufacturing process National d'Etude Spatial), Goal: Earth observation the NRL (Naval Research (type "C") the French national 1999 Laboratory) uses the 2014-2015 mapping agency (IGN, DORIS Pilot Experiment transmissions of the DORIS Contribution to ITRF2014 previously for Institut to assess the need beacons. (6 groups: IGN/JPL, CNES/ Géographique National), and feasibility of an 2008 CLS, INASAN, NASA/GSFC, and the French research International DORIS Service Jason-2 (Cnes/Nasa/ ESOC, GOP) group in the field of space Eumetsat/Noaa) with the 2016 geodesy (GRGS, Groupe de 2000-2009 Major renovation effort first DORIS receiver of the Jason-3 (Cnes/Nasa/ Recherche de Géodésie rd 3 generation (DGXX) with Eumetsat/Noaa) with the Spatiale) of the network. Objective: 1 cm over 10 years in terms 7 channels. Goal: measure 1st DGXX-S instrument. 1986 of stability of the DORIS sea surface height Goal: measure sea surface Start of the deployment of antenna reference point. 2008 height the DORIS ground network. rd Deployment of the 3 First Analysis Working 2016 32 stations with ALCATEL generation ground beacons Group meeting Sentinel-3A antenna (type "A") installed with the ability to emit on (ESA - Copernicus before Spot-2 2009 shifted frequency Start of the Combination program) Goal: deliver 1990 2001 Centre routine operational Spot-2 (Cnes) embarkes Jason-1 (Cnes/Nasa) with 2009 services to policy-makers the first DORIS instrument, the first DORIS receiver of and marine and land st Contribution to ITRF2008 1 generation with the 2nd generation with service users 1-channel receiver (7 groups: IGN/JPL, CNES/ 2 channels. Goal: measure 2018 (6–month trial experiment, CLS, INASAN, NASA/GSFC, sea surface height Sentinel-3B in use for more than ESOC, GOP, Geosciences (ESA - Copernicus 19 years). Goal of the 2002 Australia) program) Goal: deliver mission: Earth observation. Envisat (Esa). Goal: observe 2009 th routine operational Objective for DORIS: Earth's atmosphere and 4 Master Beacon services to policy-makers decimeter level orbit surface at Papeete and marine and land accuracy. First DORIS 2002 2010-today service users measurement on February Spot-5 (Cnes). Modernization of the 3rd. Goal: Earth observation network. The DORIS 2018 First IDS retreat 1990 2003 network achieves 90% DORIS Day meeting Official start of IDS as an coverage (for satellites 2019 th (December 1990, Paris) IAG Service, on July 1st. orbiting at 800 km altitude) Start of the 4 generation ground beacon deployment 1992-1999 Objective: to provide a and provides a reliable service to support geodetic service with a network Densification of the 2020 and geophysical research availability maintained over network, expanded to 54 30 years of DORIS activities through DORIS 85% of operating stations stations. Massive Alcatel measurements data and derived products since 2012 thanks to the antennas are progressively 2020 joint effort of CNES, IGN replaced by the light and 2003 HY-2C (China Academy and all agencies hosting narrow Starec model (type First IDS Governing Board of Space Technology) the stations. "B"). meeting (November 2003, Goal: observe the ocean 1992 Arles, France) 2010 dynamics Topex/Poseidon (Nasa/ 2004 3 cm orbit accuracy 2020 Cnes) Goal: measure sea 3rd Master Beacon at achieved in real time on Sentinel-6A/ Michael surface height. Objective Hartebeesthoek (South board Jason-2 Freilich (ESA - Copernicus reached by DORIS: 5-cm Africa) 2010 program) Goal: measure orbits quality in the radial 2005 Cryosat-2 (ESA); DORIS sea surface height component DORIS Integrity Team set enters the Spacecraft 2020 Attitude & Orbit Control 1993 up to monitor permanently Contribution to ITRF2020 System. Goal: polar Spot-3 (Cnes) the DORIS signal in progress observation Goal: Earth observation transmitted in space, 1994 control its characteristics, 2011 investigate non nominal HY-2A (China Academy First DORIS contribution situations, take corrective of Space Technology) to the International actions if needed. Goal: observe the ocean Terrestrial Reference dynamics Frame (ITRF); 2 groups: 2005 IGN and LEGOS/GRGS) Contribution to ITRF2005 2013 1995 (4 groups: IGN/JPL, LEGOS/ Saral/Altika (Isro/CNES) CLS, INASAN, NASA/GSFC) 2nd generation of ground Goal: observe the oceans satellites beacon network

- 4 - Newsletter of the International DORIS Service // december 2020 2020, TWO NEW MISSIONS HAVE JOINED THE DORIS CONSTELLATION

HY-2-C WAS LAUNCHED ON 21 SEPTEMBER 2020 FROM THE CHINESE LAUNCH BASE OF TAIYUAN.

HY-2 (HaiYang means "ocean") belongs to a series of Chinese oceanographic satellites started in 2011 with HY-2A, HY-2B (2018), HY-2C (September 21, 2020) and HY-2D planned in 2021. All these satellites except model "B" carry a DORIS receiver onboard. The objective of HY-2 is to monitor ocean dynamics using microwave sensors to detect wind fields at the ocean surface, sea surface height and surface temperature. CNES provides the precise orbit and retrieves the altimetry measurements which then contribute to the multi- mission maps of AVISO+ and the Copernicus Marine Service. After the commissioning phase, CNES will also distribute, the raw DORIS data (DORIS RINEX format) and the THE SENTINEL-6/JASON-CS IS precise orbits (SP3 format) to the A RESULT OF INTERNATIONAL IDS data centers. COOPERATION BETWEEN ESA, © CNES Sentinel-6A EUMETSAT, THE EUROPEAN UNION, NOAA, CNES AND NASA. SENTINEL-6A MICHAEL FREILICH (COPERNICUS- ESA/ EUMETSAT/CNES/NOAA/ and the MyOcean operational is also responsible for the expertise NASA), THE FIRST OF A oceanography project supported and evaluation of the performance TWO-SATELLITE SENTINEL-6 by the European Commission. This of the instruments and the mission. SERIES, WAS LAUNCHED BY mission is a cooperation between Sentinel-6 uses a new satellite bus A FALCON-9 ROCKET FROM ESA, the European Commission and based on CryoSat, with a capability to VANDENBERG AIR FORCE EUMETSAT. The United States is also minimize the accumulation of orbital a key partner in the mission, with debris (the de-orbiting of the satellite BASE, CALIFORNIA, ON 21 NASA and NOAA playing a role in the within 25 years is now required by NOVEMBER 2020. launch, US-side operations and the law). The Poseidon-4 altimeter will Also known as Jason Continuity of provision of a radiometer, GNSS-RO operate in the so-called ‘interleaved Service (Jason-CS), the Sentinel-6 receiver and Laser Retroreflector. mode’ that provides simultaneously satellites will replace the Jason-3 CNES, another key partner of the pulse-limited waveforms (computed satellite, thus ensuring the continuity mission, is in charge of providing on-board and in line with previous of sea level measurements and the precise orbit of the satellite (via reference missions) and Full Rate operational oceanographic services its DORIS instrument and ground RAW waveforms that allow SAR on the Topex and Jason reference station network, and the GNSS- processing on-ground. orbit beyond 2030. POD receiver), as well as the sea surface height and wave height The Sentinel-6 mission is part of products that will be used by the the European Copernicus program Copernicus Marine Service. CNES

december 2020 // Newsletter of the International DORIS Service - 5 - 2020, TWO NEW MISSIONS HAVE JOINED THE DORIS CONSTELLATION

Today there are seven DORIS • HY-2D (CNSA/NSOAS) with DORIS DGXX-S + LRA + GPS is planned for May satellites that contribute to IDS: 2021, and HY2 E-F-G-H are waiting for approval. CryoSat-2, SARAL/Altika, Jason-3, • S W O T (Surface Water Ocean Topography) is planned for the end of 2021 Sentinel-3A, Sentinel-3B, HY-2C, (DGXX-S + GPS + LRA). Further information on Swot website or on Aviso Sentinel-6A/Mike Freilich. website. • Sentinel-3C (Copernicus- ESA/ EUMETSAT/CNES) is planned for 2024 In the future, many news missions (DORIS DGXX-S with mini USO + LRA + GPS) (nominal lifetime of 7 years). are scheduled with the following Then Sentinel-3D is planned for 2025. Further information is available launches to come: on the ESA website • Sentinel-6B/Jason-CS2 is planned in 2025

More information on the International DORIS Service website (https://ids-doris.org)

- 6 - Newsletter of the International DORIS Service // december 2020

IDS LIFE

HY-2A satellite Coming soon: DORIS Meetings planned decommissioned Near-real-time DORIS data for 2021: With the end of the mission, the and DIODE orbits • February. (Virtual) Meeting of last DORIS data were delivered in The near-real-time (NRT) Analysis Centers and Associate September 2020. HY-2A has been distribution of DORIS/RINEX data Analysis Centers. Subject: part of the DORIS constellation and DIODE orbits from Jason-3 update on ITRF2020. since its launch (2011-08-15). satellite will be available in the • Late March to early April 2021. The satellite carried a DGXX near future. These NRT products (Virtual) Analysis Working Group receiver, and provided nine years will be delivered initially to the meeting. of data from its orbit at an altitude IGN Data Center; a test and • Late May, early June 2021. of 963 km and at an inclination evaluation period will follow before (Virtual) IDS School on DORIS of 99.4 deg. the availability of NRT products data and products (postponed is extended to other missions. from May 2020). DORIS network projects Interested persons should contact • October 18-20, Venice, Italy. IDS continue notwithstanding Pascale Ferrage (CNES) or Denise Workshop associated with Ocean Covid-19 Dettmering (DGFI/TUM) for more Surface Topography Science Notwithstanding the difficulties information. Team (OSTST) meeting: in maintaining the stations during https://ostst-altimetry-2021.com/ the global Covid-19 pandemic, IGN DORIS Analysis Center the ground network showed Arnaud Pollet and Samuel good operating results thanks Nahmani will lead the IGN/DORIS to the 4th generation beacon Analysis Center activities following deployment started last year to the retirement of Pascal Willis. firstly replace old equipment with signs of weakness. Most of the development projects are at a Some noteworthy DORIS-related publications in 2020 standstill but, fortunately, some advances were made in Europe 1. Bertiger, W., Bar-Sever, Y., Dorsey, A., et al. (2020). “GipsyX/RTGx, a this summer: new DORIS site in new tool set for space geodetic operations and research”, Adv. Space Höfn, Iceland in place of Reykjavik Res., 66(3), 469-489, doi:10.1016/j.asr.2020.04.015. (commissioned September 24th); 2. Zhou, C.C., Zhong, S.M., and Peng, B.B., et al. (2020). “Real-time orbit reconnaissance in Crete, Greece determination of Low Earth orbit satellite based on RINEX/DORIS 3.0 for an additional station. We thank phase data and spaceborne GPS data”, Adv. Space Res., 66(7), 1700- all the host agencies for their 1712, doi:10.1016/j.asr.2020.06.027. ongoing efforts to keep the DORIS 3. Hernandez-Pajeres, M., Lyu, H.X., Garcia-Fernandez, M. and R. Orus- station operating! Perez (2020). “A new way of improving global ionospheric maps by Access to DORIS data ionospheric tomography: consistent combination of multi-GNSS and and products multi-space geodetic dual-frequency measurements gathered from vessel-, LEO- and ground-based receivers”, J. Geodesy, 94(8), 73, The NASA CDDIS Data Center doi:10.1007/s00190-020-01397-1 stopped providing anonymous ftp services as of 1 November 2020. 4. Stepanek, P., Bingbing, D., Filler, V. and U. Hugentobler, (2020). All users are now requested to “Inclusion of GPS clock estimates for satellites Sentinel-3A/3B in use https, and an NASA Earthdata DORIS geodetic solutions”, J. Geodesy, 94:116, doi:10.1007/s00190- login as a method of access to the 020-01428-x. CDDIS archive. Instructions and 5. Beutler, G., Villager, A., Dach, R., Verdun, A., and A. Jäggi (2020). example links are available here: “Long polar motion series: Facts and insights”, Adv. Space Res., https://cddis.nasa.gov/Data_and_Derived_ Products/CDDIS_Archive_Access.html 66(11), 2487-2515, doi: 10.1016/j.asr.2020.08.033. Unencrypted anonymous ftp services are still available at IGN A full list of articles related to DORIS published since 1985 is available on the IDS website at Data Center for the time being: https://ids-doris.org/ids/reports-mails/doris-bibliography/peer-reviewed-journals.html ftp://doris.ign.fr/

december 2020 // Newsletter of the International DORIS Service - 7 - PASCAL WILLIS RETIRES

the analysis of DORIS data and the Centers’ Representative. In this development of better DORIS-derived capacity, he was elected and served geophysical products. He worked to as Chairperson from 2009 to 2016. improve precise orbit determination Throughout his career, Pascal worked with DORIS data throughout his tirelessly to promote and improve the career. Pascal directed an analysis contribution of DORIS as one of the center for DORIS at the IGN that four techniques of space geodesy. regularly submitted geophysical products and contributed to ITRF Pascal’s non-DORIS professional realizations. He worked to interpret contributions also included the time series of coordinates for being an early advocate of the science and geophysics. He also scientific contributions of other After a long and active career worked to promote new products GNSS constellations (GLONASS promoting analysis and use of from DORIS data, collaborating with & Galileo). He led the IGEX-98 DORIS data in geodesy, Dr. Pascal researchers to promote DORIS as a campaign for GLONASS as part of his Willis retired from the Institut tool for to use troposphere delays responsibilities being a member, at Géographique National (IGN) in April for climate studies. As part of his the time, of the Governing Board of 2020. Pascal and his wife, Michèle research activities he co-directed the (then) International GPS Service have retired to their new domicile, or directed the Ph.D work of (IGS). As a guest editor for GLONASS near La Rochelle, France. Pascal Jean-François Crétaux (Ph.D, 1993), and Galileo special issues in the remains active as Editor-in-Chief Laurent Morel (Ph.D, 2001), Stéphane Journal of Geodesy (2000-2001) of the journal, Advances in Space Durand (Ph.D, 2003) and Marie-Line and Advances in Space Research Research. In this capacity, people in Gobinddass (Ph.D, 2010). (2009-2010) he helped to elevate the DORIS community can continue the contributions of these navigation to take advantage of his advice and A career devoted systems in the scientific community. suggestions regarding the research to geodesy Since 1995 Pascal has served they would like to publish. continuously as an Associate Editor Pascal Willis forged a tight or Guest Editor for different scientific Pascal received degrees as engineer collaboration with the Jet Propulsion journals and International Association from the École Polytechnique Laboratory (JPL) from the early days Geodesy (IAG) proceedings volumes. (1983) and the École Nationale des of the TOPEX/Poseidon mission. He Many readers will be familiar with Sciences Géographiques (1986). used the JPL GIPSY/OASIS II software this pointed and detailed reviews In 1989, he received his Ph.D from to process DORIS data, working of their papers, always aimed to the Paris Observatory with a thesis closely with JPL to maintain and improving the quality of science focused on “The Static and Kinematic continually improve this capability. He communication. Applications of GPS for Geodesy”. worked at JPL as a visiting scientist He received his “Habilitation à from 2001-2006, and in recent years We will miss Pascal as a regular Diriger des Recherches (HDR)” in collaborated with Dr. William Bertiger participant in the IDS. We 2003 from the Université Pierre et and other scientists at JPL to validate congratulate Pascal on his retirement Marie Curie (Paris VI)1. His initial the processing of DORIS/RINEX data and wish both him and his wife professional work was with GPS, but in the new JPL GipsyX software. Michèle enjoyable and exciting he became more focused on the explorations in the coming years. analysis of DORIS data starting with Pascal Willis was one of the co- 1. In some countries (such as France) the TOPEX/Poseidon mission. His founders of the International DORIS a “Habilitation” is required to conduct work concentrated on how to apply Service (IDS) in 2003, and served university teaching, direct research or methodological improvements to on the Governing Board as Analysis become a university professor.

PUBLICATION DIRECTOR: IDS P. FERRAGE 11 RUE HERMÈS EDITOR-IN-CHIEF: L. SOUDARIN PARC TECHNOLOGIQUE DU CANAL CONTRIBUTORS TO THIS ISSUE: 31520 RAMONVILLE SAINT-AGNE P. FERRAGE, F. LEMOINE, FRANCE J. SAUNIER, L. SOUDARIN DESIGN: STUDIO OGHAM Flash here to visit the IDS website

- 8 - Newsletter of the International DORIS Service // december 2020